1. Field of the Invention
The invention relates to a drive apparatus for a hybrid vehicle that is preferably used in a hybrid vehicle provided with an engine and an electric motor, which are two types of power sources having different characteristics, and which runs by using the driving power from these two power sources in a combination that is optimal for the conditions.
2. Description of the Related Art
In recent years a hybrid vehicle provided with an engine and an electric motor, which are two types of power sources having different characteristics, has been developed and put into practical use. In this hybrid vehicle, the strengths of each power source are used to compensate for the weaknesses of the other by using the driving power from the type types of power sources in a combination that is optimal for the conditions. As a result, the power performance of the vehicle is able to be sufficiently ensured and the fuel consumption rate and emission performance are able to be largely improved.
Various proposals have been made for the drive apparatus to be used in this type of hybrid vehicle. One proposal includes the use of a first motor generator, a power splitting mechanism portion, and a second motor generator. The first motor generator serves mainly as a generator. The power splitting mechanism portion includes a planetary gear set and divides the power generated by the engine into power for the first motor generator and power for the driven wheels. The second motor generator serves mainly as a motor and generates power to assist in driving the driven wheels. This power is different from the power that is from the engine.
In this drive apparatus, part of the power that has been split by the power splitting mechanism portion is transmitted mechanically to the driven wheel to rotate it, and the rest of the power that has been split is transmitted to the first motor generator. Using the power transmitted to the first motor generator, the first motor generator functions as a generator and generates electricity which is supplied to the second motor generator. Using this electricity, the second motor generator functions as a motor. The power generated by this second motor generator is added to the power that was split by the power splitting mechanism portion and transmitted to the driven wheel, thereby assisting the output of the engine in driving the driven wheel.
Also, as art relating to the layout of each of the component parts in the drive apparatus for a hybrid vehicle, art in which a first motor generator, a second motor generator, and a planetary gear set are arranged in-line is disclosed in Japanese Patent Application Laid-Open Publication No. 6-144020. This arrangement is advantageous in that the build, more particularly the outside diameter, becomes gradually smaller farther away from the engine, thereby enabling the entire apparatus to be made compact.
With the drive apparatus for a hybrid vehicle, it is conceivable to add a speed reducing mechanism portion to reduce the rotation speed and to increase the torque of the second motor generator which serves as the motor. With the drive apparatus disclosed in the aforementioned publication, however, a layout when this speed reducing mechanism portion is added to the planetary gear set as a power splitting mechanism portion is not shown in detail. Therefore, there is a desire for a drive apparatus in which the entire apparatus, including this speed reducing mechanism portion, can be made compact.